74 The American Naturalist. [January, 
and there in the inner mass of all solid sponge larve, and disappears — 
during metamorphosis. It is probably concerned in maintaining the — 
equilibrium of the larva. i 
Metamorphosis.—It is commonly believed that the ciliated cells of the — 
larva flatten and become the epidermis of the adult, but Delage finds 
that the former absorb their cilia, assume a rounded shape and migrate 
into the interior, their place being taken by the epidermic cells which — 
fuse with one another so as to form a complete membrane. Only over ~ 
the non-ciliated pole of the larva does this inter-change of cells fail to 
take place, for here the epidermic cells have all along been at the sur- ; 
The ciliated cells that migrate into the interior are destined to — 
become the collared cells of the flagellated chambers. The interval — 
between their immigration and the formation of the chambers is marked — 
by a curious association of these cells with the ameboids. The latter 
elements engulf, amceba-fashion, the former. Complete fusion takes 
place between the bodies of the amoeboid and the absorbed cells, but — 
the nuclei of the latter remain distinet, and range themselves round — 
the larger nucleus of the amoeboid. (Multivucleate cells, whether — 
formed in this way or not, undoubtedly exist in the developing sponge. r 
They were observed by Götte (1888) who regarded the smaller bodies 
contained in them and arranged round the larger central one, %& 
deuto-plastic structures, which become nuclei. Moss (1890) regards — 
the small peripheral bodies simply as deutoplastic structures. Wilson — 
(1891) describes them as nuclei). In Spongilla all the ciliated are50 
absorbed. In the other sponges only a portion are so absorbed. ae 
rest unite with one another and with the (now) multinucleate amoeboids - 
to form asyncitium. To form a flagellated chamber several multi- 
nucleate masses approach one another so as to surround a central spacer 
the cavity of the futurechamber. The nuclei of the absorbed (ciliated) — 
cells arrange themselves round this cavity and cell bodies are differenti 
ated about them, while the nucleus of the original amceboid cell, sur- 4 
rounded by protoplasm, escapes from the anlage of the chamber, and be- ; 
comes one of the wandering cells of the adult mesoderm (the review 4 
l. Cy has shown that chambers are sometimes formed by the fusion © — 
multinucleate masses, but has also shown that chambers may be simulta- 
neously formed by aggregations of amoeboid or “ formative” cells, which 
may or may not be multinucleate, The two processes are regarded tae 
fun illy the same. Such observations would seem to contradict 
the author’s thesis that it is the immigrated ciliated cells which form the 
